Kerber seized the early initiative as her power wore the eighth seed's backhand down and secured a 3-1 lead, before Bertens further felt the weight of her opponent's pressure and an error-strewn service game ended with a forehand long and a second break.

The opening set settled, further Bertens errors - including another costly double fault - resulted in an effortless break at the start of the second.

However, a first wobble from Kerber opened the door for Bertens to level up the set with a smash into the open court at the net, before a pivotal game went against the favourite and another break followed.

The Wimbledon champion believed she had accurately measured a lob on the stretch, celebrating a point to clinch the game, but the decision went against her and she lost her appeal, granting Bertens the opportunity to push hard and break through against an uncharacteristic double fault.

That was enough for Bertens to tie the match with her serve and the now confident underdog charged into the lead with a swift break in the third.

Yet in an extraordinary stretch that saw both players apparently lose composure, that was the first of seven games to go against serve at the start of the final set.

It was Bertens who emerged with the advantage, though, and a crucial hold with an ace teed up an impressive triumph, showing her worth in Singapore at this early stage as the lower seed won for the fourth straight Finals match.